What's wrong with my rabbit :'(?

My rabbit is a 9months old female and recently (for about 3 days now) she's been biting the metal bars of her pen and then making soft grunting noises when she's let out.

I make sure she always has enough food and hay and water in her pen and that the pen is cleaned every other day but she still keeps biting her pen's metal bars. I thought she might just want to be let out and run around so i let her out for about 3hrs everyday (i've read that that should be enough on a webpage). I've just let her out again now and she's making soft grunting noises and seems to be looking for something: she jumps around and licks things (including my arm). I don't know what's happening or what i should do! Please help!